Researchers from three continents have developed a thin, scratch-resistant coating that they claim can be easily created in any color without use of pigments.The team is led by Harvard University’s Henning Galinski and includes researchers from King Abdullah University of Science and Technology (Saudi Arabia) and ETH Zurich (Switzerland). The concept is based on structural coloration. This is a phenomenon seen in bird feathers, such as those of a peacock, or the wings of butterflies, whereby biological nanostructures allow seemingly colorless materials to reflect light in ways that create a colorful appearance. The research team says it’s a major step toward scalable versions of the technology, which could have applications from buildings to cars and airplanes. The idea of structural coloration involves The new development involves spraying a platinum-aluminum alloy onto the substrate, then ‘de-alloying,’ or removing most of the aluminum, and ultimately combining “de-alloyed subwavelength structures at the nanoscale with loss-less, ultra-thin dielectrics coatings.” The coating begins as transparent. Then, an ultra-thin layer of sapphire is infused into the coating. Sapphire is an especially hard mineral, already used in glass to make scratch-resistant windows and screens for electronics. The sapphire lends hardness and abrasion-resistance to the coated surface, and also engenders the color-shifting abilities of the coating. The thickness of the sapphire determines the color the coating takes on, because the sapphire particles fill nanopores in the coating in different ways at different thicknesses. Changing the thickness of the layer at the nano scale can generate any desired color, and because the coloration is part of the material structure, it won’t fade. Unlike recent developments in coatings that can change color on demand, the coating isn’t ever-changing. It can, however, be tailored to any color needed, without pigments or additives. The color is ‘programmed’ into the coating as it is applied, meaning one batch of coating material could create any number of colors using the same process. Because the coating is thin, durable and can produce any color on demand, it could be used for architectural applications and beyond. The researchers say the technology could find a place in the automotive recoat industry, or even aerospace coatings.